Slide element and method for production of said slide element

ABSTRACT

The invention relates to a gliding element with a substrate and a diamond layer formed on a surface of the substrate with an average maximum roughness value Rz. To improve the dry running properties the invention suggests that the diamond layer has reproducible recesses for the collection of abrasion, wherein a depth of the recesses is greater than the average maximum roughness value Rz.

The invention relates to a gliding element as defined in the preamble ofclaim 1. Moreover it relates to a method of manufacturing the glidingelement.

A gliding element of this type is known from U.S. Pat. No. 5,108,813 aswell as from WO 00/26433. To reduce the friction coefficient and theabrasion of the diamond layer it is suggested that the gaps createdbetween the diamond crystals be filled with a soft metal. In actualpractice, however, it has been shown that the filling consisting of thesoft metal wears off relatively quickly. This causes the gliding elementto lose its anti-frictional properties.

From EP 0 529 327 A1 a fired ceramic product with a structured surfaceis known. To improve the tribological properties it is suggested to formthe structuring in a regular arrangement of uniform depressions.Although the fired ceramic product exhibits good tribologicalproperties, the resistance to abrasion is not sufficient for extremeloads.

From EP 0 617 207 B1 a bearing is known on which tribological stressedcontact surfaces facing one another are provided with a diamond layer.Such a bearing does not have sufficient dry running and anti-frictionalproperties for certain applications.

From DE 197 16 330 A1 a method is known for the manufacture of a coatingon a grinding tool. There it is suggested that the diamond layer be madeparticularly rough. Such a diamond layer is not suitable for themanufacture of tribologically stressed surfaces for sliding rings orbearings.

From EP 0 614 999 B1 a component of a bearing or a sealing arrangementis known on which a wear surface is formed from a layer made ofpolycrystalline diamond. The diamond layer is formed so that itstribologically stressed surface has a reduced resistance to wear. Forthis purpose the surface is formed from a soft nano-crystalline diamondlayer which is located on a hard polycrystalline diamond layer. Inactual practice such a diamond layer does not have adequateanti-frictional and dry running properties.

Especially in the area of highly stressed components, particularly withsliding bearings and sliding ring seals, improved anti-frictional anddry running properties are desired. Particularly during dry running,very high friction coefficients and/or friction coefficient fluctuationsoccur suddenly. Such friction coefficients and/or friction coefficientfluctuations also destroy gliding elements which are coated with aconventional diamond layer.

The object of the invention is to remove the disadvantages as defined inthe state of technology. In particular a gliding element is to bespecified which has improved anti-frictional and dry running properties.Furthermore a method is to be provided for the manufacture of such agliding element.

This object is solved by the features of claims 1, 13 and 14. Usefulembodiments result from the features of claims 2 to 12 and 15 to 28.

According to the invention it is provided that the diamond layer hasreproducible recesses to hold abrasion wherein the depth of the recessesis greater than the average maximum roughness value Rz.

Surprisingly such a gliding element exhibits drastically improvedanti-frictional and dry running properties. According to the currentstate of knowledge this is thought to be due to abrasion consisting ofnano-crystalline diamond and graphite is formed particularly during dryrunning. With conventional diamond layers the abrasion collects on thesurface in the depressions between the diamond crystals. As soon as alldepressions are filled, a drastic increase of the friction coefficientis observed. This destroys the diamond layer. By supplying recessesaccording to the invention in the diamond layer the depth of whichrecesses is greater than the average maximum roughness value Rz, morespace is created for holding the abrasion. The anti-frictional and dryrunning properties are drastically improved.

In the sense of DIN EN ISO 4287 “average maximum roughness value Rz”means the maximum roughness profile height. This is the sum of theheight of the highest profile peak Rp and the depth of the greatestprofile valley Rv of the roughness profile within a single measuringlength.

As vertical distance from the utmost to the deepest profile point, Rz isa unit of measure for the scattering range of the roughness ordinatevalues. Rz is calculated as the arithmetic average from the maximumprofile height of 5 single measuring lengths lr in the roughnessprofile.

The recesses suggested by the invention are not recesses which werecreated by chance when the diamond layer was made. These are recesseswhich are manufactured reproducibly, preferably in a specifiedarrangement. The recesses can be incorporated in the diamond layer afterthe diamond layer is manufactured. However it is also possible that therecesses are incorporated in a surface of the substrate before thediamond layer is applied. The recesses provided by the invention clearlydiffer in their dimensions from the depressions, for example gaps,created between the diamond crystals. The recesses provided by theinvention have a greater depth than the depressions.

It is useful that the average maximum roughness value Rz is in the rangefrom 0.1 to 5.0 μm. Diamond layers with such an average maximumroughness value Rz are particularly suitable for the manufacture ofsliding ring seals and sliding bearings. Diamond layers with such anaverage maximum roughness value Rz also do not show a particularly highamount of abrasion during dry running. In any case the abrasion is soslight that it can be retained in the recesses provided by theinvention. It is useful that the recesses have a depth of 0.2 to 100 μm,preferably 0.5 to 50 μm. A surface of the recesses can be made ofgraphite. This simplifies removal of the abrasion contained in therecesses.

It is useful that the recesses have linear structures. The recesses canin particular be straight or crescent-shaped. It is useful that thelinear structures run slanted or crosswise to a sliding direction. Asdefined in a further arrangement the recesses can open towards the edgeof the diamond layer so that the collected abrasion can be removed.Removal of the abrasion at the edge of the diamond layer furtherincreases the anti-frictional and dry running properties of the glidingelement.

A width of the recesses can be between 0.5 μm and 10 mm. Further it hasbeen shown to be useful that the recesses have a net-like pattern or arealso trough-like.

It is advantageous that a portion of 1 to 95% of the surface of thediamond layer is formed by the recesses. The recesses can thus also forman essential portion of the surface. A tribologically stressed contactsurface of the diamond layer consists in this case only of single,preferably regularly spaced, islands.

According to a further embodiment the substrate is made from a ceramic,preferably SiC, or from a metal or a metal-ceramic composite material.

To make a gliding element as provided by the invention a method can beperformed with the following steps according to a first version:

Apply a diamond layer with an average maximum roughness value Rz to asurface of the substrate and Make recesses in the diamond layer suchthat a depth of the recesses is greater than the average maximumroughness value Rz.

According to a second version a method with the following steps isprovided for the making of a gliding element as defined in theinvention:

Make recesses of a specified depth in the surface of the substrate and

Apply a diamond layer to the surface such that an average maximumroughness value Rz of the diamond layer is less than the depth of therecesses.

The suggested method is relatively simple to execute.

The diamond layer is usefully applied via a CVD method to the surface.Such methods are known according to the state of technology and aredescribed in literature, for example, in K. Bachmann, W. van Enckewort,“Diamond Deposition Technologies” in Diamond and Related Materials (1),1992, S. 1021-1034.

The recesses can be made mechanically by etching or via LASER. They canalso be made by smoothing the diamond elevations created during themaking of the diamond layer. Such diamond elevations protrude out fromthe diamond layer. By smoothing, these elevations are removed and brokenoff. The smoothing can be done by lapping.

According to a further particularly advantageous embodiment the surfaceof the recesses can be converted to graphite thermally, preferablyduring manufacturing via LASER. In particular with a linear embodimentof the recesses which open towards the edge of the diamond layer agraphite layer in the recesses makes it easier to remove the abrasion.

For the further advantageous embodiments of the method, reference ismade to the embodiments described for the gliding element. These alsoapply accordingly to the method.

Based on the drawings, advantageous embodiments of the inventions willnow be described in more detail. The figures are listed below:

FIG. 1 A scanning electron microscope (REM) image of a diamond layeraccording to the state of art,

FIG. 2 a-c REM images of the diamond layers according to the inventionin different enlargements,

FIG. 3 A presentation in perspective of a diamond layer according to theinvention,

FIG. 4 a, b Schematic presentations of different recess patterns,

FIG. 5 The result of a dry running test using a conventional diamondlayer,

FIG. 6 The result of a dry running test using a diamond layer accordingto the invention,

FIG. 7 A REM image of a conventional diamond layer with diamondelevations,

FIG. 8 A REM image of a further diamond layer according to theinvention,

FIG. 9 a Results of different measurements during dry running and

FIG. 9 b A schematic presentation of the processes taking place duringdry running.

FIG. 1 shows a REM image of a surface of a conventional diamond layerwhich has been deposited via a CVD method on a substrate, for exampleSiC. The topography of the surface is characterised by the {111} and{100} areas of the diamond crystals. Depressions are located between thediamond crystals. The average maximum roughness value Rz of the shownconventional diamond layer is 1.1.

FIG. 2 a to FIG. 2 c show REM images in various enlargements of adiamond layer according to the invention. Also here the diamond layerhas an average maximum roughness value Rz of 1.1. Moreover linearrecesses V are provided running at a slant to a sliding directionlabelled T which recesses extend over the entire width of the diamondlayer. The recesses V are arranged at regular intervals; they formparallel lines with a constant distance. FIG. 3 again shows inperspective the formation of the diamond layer.

It is useful that the thickness of the diamond layer for the glidingelements according to the invention is between 0.1 μm and 50 μm,preferably 1 to 20 μm. With this a diamond layer with a <111> texturesetting is preferred. For an explanation, reference is made to DE 100 27427.7 whose disclosed contents are included herewith. In addition atexture of <110> can also be set. With the design example shown in FIG.2 and FIG. 3 the layer thickness of the diamond layer is 12 μm. Thewidth of the linear recesses V is approximately 20 μm and the depth ofthe recesses V is approximately 5 μm. With this design example the depthof the recesses V is thus approximately 4.5 times the average maximumroughness value Rz. In general it has proved to be useful that the depthof the recesses V is greater than twice, preferably greater than 3 timesand, particularly preferably, greater than 4 times the average maximumroughness value Rz.

FIGS. 4 a and b show a sliding ring with a diamond layer. Also herelinear recesses V are provided in turn on the diamond layer. With thesliding ring shown in FIG. 4 a the recesses V are arranged parallel toeach other at regular intervals. With the sliding ring shown in FIG. 4 bthe recesses run from an inner circumferential surface to an outercircumferential surface slanted towards the radial direction.

FIGS. 5 and 6 show the results of the dry running test in comparison.The particular friction coefficient is entered over the friction path.The results shown in FIG. 5 were obtained using sliding rings which arecoated with a diamond layer as they are shown in FIG. 1 for example. Theresults shown in FIG. 6 were obtained using sliding rings which arecoated with a diamond layer as provided by the invention which layer isshown in FIG. 2 to 4 for example. With the measurements the surfacepressure is 0.2 N/mm², the rotation speed is 1.3 m/s and the run time is4 hours. It is shown that the gliding elements coated with the diamondlayers according to the invention have drastically better dry runningproperties. The diamond layer is still completely intact after a testtime of 4 hours. No layer chipping at all can be observed.

FIG. 7 shows a REM image of a conventional diamond layer made by a CVDmethod. Such diamond layers often have elevations E. Such elevations Eare usually not desired. According to the subject of this invention,diamond layers with such elevations E can nevertheless also be used tomake gliding elements as provided by the invention.

FIG. 8 shows a REM image of a diamond layer of a gliding element asprovided by the invention. The layer is made by removing the elevationsE shown in FIG. 7 via lapping, for example. Elevation stubs Es remain.In this sample design a tribologically stressed surface is formed onlyby the sum of the elevation stubs Es protruding out over the surface ofthe diamond layer. The abrasion that occurs during operation can bedeposited here around the elevation stubs Es. Naturally the elevationstubs Es shown in FIG. 8 can also be combined with the recesses shown inFIG. 2 to 4 for example. In this case the suggested gliding elementshave excellent running in properties. The relatively high wear whichoccurs during running in causes the elevation stubs in particular towear down. The abrasion is transported during run-in to the recesses V.With this the surface of the diamond layer is hardly damaged since theelevation stubs Es rise above this. After running in, the elevationstubs Es are essentially worn off. The wear caused by the running in ispartially contained in the recesses. The diamond layer is hardly worn bythe running in. It has a particularly long life. In addition thedifferences in layer thickness created by the deposit of the diamondlayer can be equalised by the elevation stubs Es.

FIG. 9 a shows various measuring results on the friction path. Thisinvolves the temperature in ° C., the distance of the friction surfacein μm and the friction number μ. The results show the effects of anabrasion incorporated between the friction surfaces. If the abrasiongets between the friction surfaces, the temperature increases and thedistance of the friction surfaces increases. At the same time thefriction number jumps up suddenly.

FIG. 9 b shows schematically the development of a conventional diamondlayer during dry running. First the crystal points of the diamondcrystal D (FIG. 9 b (i)) break. The abrasion A created by thispenetrates between the depressions Z created between the diamondcrystals (see FIG. 9 b (ii)). As soon as the depressions Z arecompletely filled with abrasion A (see FIG. 9 b (iii)), the abrasion Ais moved to the surface. After a short time catastrophical wear occurs,in particular the diamond layer chips off thus causing the glidingelement to fail.

The manufacture of the gliding elements as provided by the invention canalways be performed in two ways. According to the first method asubstrate, made of SiC for example, is first provided. Recesses V arethen incorporated into the substrate in the conventional way. This canbe done by mechanical removal with diamond-coated tools. Removal is alsopossible via conventional LASER. In any case recesses V are incorporatedinto the surface of the substrate in a specified arrangement. Withrecesses V this can be ditch-like structures or troughs. The recesses Vusefully form a specified regular pattern. They have a depth of 2 to 10μm and a diameter or a width of 8 to 30 μm. The thus prepared substrateis then coated via the conventional CVD method. The layer thickness ofthe applied diamond layer is 8 to 10 μm. The parameters are set so thatthe recesses V incorporated into the substrate before are imaged by thediamond layer.

According to a second method the recesses V are also first made afterthe application of the diamond layer. For this purpose the recesses arealso mechanically worked into the surface of the diamond layer, forexample with saws or preferably via laser processing. With laserprocessing a conversion of the processed surfaces into graphite takesplace. This creates particularly smooth recesses through which theabrasion can easily be transported away.

REFERENCE DESIGNATION LIST

-   T Transport direction of the abrasion-   V Recess-   E Elevation-   Es Elevation stub-   D Diamond crystal-   Z Gap-   A Abrasion

1. Gliding element with a substrate and a diamond layer formed on asurface of the substrate with an average maximum roughness value Rz,characterised thereby that the diamond layer has reproducible recesses(V) for the holding of abrasion (A) wherein a depth of the recesses (V)is greater than the average maximum roughness value Rz.
 2. Glidingelement as defined in claim 1, wherein the average maximum roughnessvalue Rz is in the range from 0.1 to 5.0 μm.
 3. Gliding element asdefined in claim 1, wherein the recesses (V) have a depth of 0.2 to 100μm.
 4. Gliding element as described in claim 1, wherein a surface of therecesses (V) is formed from graphite.
 5. Gliding element as defined inclaim 1, wherein the recesses (V) have linear structures.
 6. Glidingelement as defined in claim 1, wherein the linear structures run at oneof: a slant and crosswise to a sliding direction (T).
 7. Gliding elementas defined in claim 1, wherein the recesses (V) open towards the edge ofthe diamond layer so that the abrasion (A) collected therein can beremoved.
 8. Gliding element as defined in claim 1, wherein a width ofthe recesses (V) is between 0.6 μm and 10 mm.
 9. Gliding element asdefined in claim 1, wherein the recesses (V) form a net-like pattern.10. Gliding element as defined in claim 1, wherein the recesses (V) havea trough-like form.
 11. Gliding element as defined in claim 1, wherein aportion of from 1 to 95% of the surface of the diamond layer is formedby the recesses (V).
 12. Gliding element as defined in claim 1, whereinthe substrate is made from one of: a ceramic, SiC, a metal and ametal-ceramic composite material.
 13. Method for the manufacture of agliding element comprising the following steps: applying a diamond layerwith an average maximum roughness value Rz to a surface of a substrateand manufacturing recesses (V) on the diamond layer such that a depth ofthe recesses (V) is greater than the average maximum roughness value Rz.14. Method for the manufacture of a gliding element comprising thefollowing steps: manufacturing recesses (V) of a specified depth of asurface of a substrate and applying a diamond layer on the surface suchthat an average maximum roughness value Rz of the diamond layer issmaller than the depth of the recesses (V).
 15. Method as defined inclaim 13, wherein the diamond layer is applied to the surface with a CVDmethod.
 16. Method as defined in claim 13, wherein the recesses (V) aremechanically made by etching or via LASER.
 17. Method as defined inclaim 13, wherein the recesses are made by smoothing of the diamondelevations (E) created during the manufacture of the diamond layer. 18.Method as defined in claim 13, wherein the average maximum roughnessvalue Rz is in the range from 0.1 to 5.0 μm.
 19. Method as defined inclaim 13, wherein the recesses (V) are made with a depth of 0.2 to 100μm.
 20. Method as defined in claim 13, wherein a surface of the recesses(V) is thermally converted to graphite, preferably during themanufacture via LASER.
 21. Method as defined in claim 13, wherein therecesses (V) are formed as linear structures.
 22. Method as defined inclaim 13, wherein the linear structures run at one of: a slant andcrosswise to a sliding direction (T).
 23. Method as defined in claim 13,wherein the recesses (V) are manufactured open towards the edge of thediamond layer so that the abrasion (A) collected therein can betransported away.
 24. Method as defined in claim 13, wherein the linearstructures are manufactured between 0.5 μm and 10 mm.
 25. Method asdefined in claim 13, wherein the recesses (V) are formed as a net-likepattern.
 26. Method as defined in claim 13, wherein the recesses (V)have a trough-like form.
 27. Method as defined in claim 13, wherein aportion from 1 to 95% of the surface of the diamond layer is formed bythe recesses (V).
 28. Method as defined in claim 13, wherein thesubstrate is made of one of: a ceramic, SiC, a metal or a metal-ceramiccomposite material.